The present invention relates to caging systems for housing and isolating laboratory animals, and in particular to cage assemblies for the breeding of colonies of mice, rats or other small laboratory animals or for laboratory experimental work with such animals. Each of the cage assemblies includes a see-through cap or bonnet which has a detachable reusable filter, and remains securely in place on the cage body without being fastened thereto, to function as an effective microbiological barrier.
In the production of colonies of mice or other small laboratory animals by breeding, the mice are housed in animal cages which are arranged in close proximity within confined areas. The colonies are subject to air-borne diseases which spread rapidly from one cage to another, particularly where the surrounding environment is not particularly sanitary. It is particularly desirable to maintain a closed, limited Defined Flora colony, that is a colony of mice having a limited number of bacteria which are constantly the same. It has hitherto been impossible to maintain a constant flora over long periods of time without employing complex isolator systems which are expensive and not economically feasible in the breeding production of laboratory mice.
The same problems are encountered in the maintainence of the animals during laboratory experimental work. Although the surrounding environment is more sanitary, the animals are housed in open cages which are arranged in close proximity to each other, usually on multi-tier racks. The animals in the different cages may be infected with various selected diseases while others may be uninfected for comparison purposes. It has been difficult or impossible to prevent the spread of diseases from one cage to another without employing complex isolator systems.
Conventional cages for small laboratory animals are usually of the open-mesh type in which the cage side and bottom walls are made of wire grill or perforated metal, or of the "shoebox" type having solid imperforate side and bottom walls made of transparent plastic material, and an open top. The cage assembly of the invention herein is directed to the latter type of "shoebox" transparent cage body, in combination with a filter cover therefor. The cage body may include a removable lid made of a grid of straight spaced bars, and shaped to contain hoppers for the storage of food and water which are easily accessible to the animals within the cage. The term "cage", as used in this description, generally refers to a cage body or tray having solid side and bottom walls and an open top, with the optional inclusion of a grid-type lid overlying the open top and having means for mounting water and food containers.
In the use of such cages for animal production or experimental laboratory research, it is imperative that bacteriological conditions established in an individual cage be maintained for as long as such conditions are desired. It is also desirable to have a clear view of the animals through any top cover provided for the cage, since other portions of the cage are occasionally obstructed.
Attempts to accomplish these objectives are well known in the art. For example, U.S. Pat. No. 3,343,520 discloses a disposable animal cage filter cover having a body formed of glass fibers and polyvinyl chloride. The filter cover is made from a blank that is cut into several panels, folded and assembled or made from a collapsible construction. Cut-outs are included in the filter cover for transparent window members. This structure is not autoclavable and its sterility at the time of use cannot be assured. Furthermore, the cover can be easily dislodged during use, thereby upsetting the microbiological conditions in the cage. In addition, the recurring expense associated with such a structure as well as the establishment of a safe disposal procedure for the covers after their use are further problems that must be dealt with.
U.S. Pat. Nos. 3,528,227, 3,528,390 and 3,613,639 show animal cage covers that are molded in one piece from a fibrous web material, such that the entire cover constitutes a filter. Although these covers can be reused, they are opaque, light-weight and tend to dislodge on the cage, especially when one cage is placed in close proximity to another where abutment of adjacent cage covers is likely.
It is thus desirable to provide a reusable filter cap or cover for an animal cage that has the microbiological integrity of a complex isolator without high cost or awkward limitations on the movement of people and animals. It is also desirable that such cap permit viewing of the encaged animals and be autoclavable.
It is an object of the present invention to provide an animal cage filter cap which is constructed to be removably mounted in secure position upon standard animal cages having solid transparent walls, and which provides with the cage an effective microbiological barrier for the animals housed therein, and minimizes the emission of animal odors from the cage by maintaining limited defined anaerobic bacterial flora.
Another object of the invention is the provision of an animal cage filter cap of the type described which is reusable and which mounts a removable and reusable filter, both the cap body and filter being capable of being autoclaved.
Another object of the invention is to provide an animal cage filter cap of the character described which is transparent so that the housed animals can be observed therethrough, and which is rigid, durable, easy to handle, easy to sterilize, uses minimal rack space, and does not dislodge when adjacently-disposed cages are pushed against one another during handling.
A further object of the invention is the provision of an animal cage filter cap of the character described which is incorporated in a novel cage assembly and caging system which is simple to use, inexpensive to produce, and allows easy access to selected cages without time consuming entry procedures.